Spectroscopic imaging combines digital imaging and molecular spectroscopy techniques, which can include Raman scattering, fluorescence, photoluminescence, ultraviolet, visible and infrared absorption spectroscopes. When applied to the chemical analysis of materials, spectroscopic imaging is commonly referred to as chemical imaging. Instruments for performing spectroscopic (i.e. chemical) imaging typically comprise image gathering optics, focal plane array imaging detectors and imaging spectrometers.
In general, the sample size determines the choice of image gathering optic. For example, a microscope is typically employed for the analysis of sub micron to millimeter spatial dimension samples. For larger objects, in the range of millimeter to meter dimensions, macro lens optics are appropriate. For samples located within relatively inaccessible environments, flexible fiberscopes or rigid borescopes can be employed. For very large scale objects, such as planetary objects, telescopes are appropriate image gathering optics.
For detection of images formed by the various optical systems, two-dimensional, imaging focal plane array (FPA) detectors are typically employed. The choice of FPA detector is governed by the spectroscopic technique employed to characterize the sample of interest. For example, silicon (Si) charge-coupled device (CCD) detectors or CMOS detectors are typically employed with visible wavelength fluorescence and Raman spectroscopic imaging systems, while indium gallium arsenide (InGaAs) FPA detectors are typically employed with near-infrared spectroscopic imaging systems.
A variety of imaging spectrometers have been devised for spectroscopic imaging systems. Examples include, without limitation, grating spectrometers, filter wheels, Sagnac interferometers, Michelson interferometers, Twynam-Green interferometers, Mach-Zehnder interferometers, and tunable filters such as acousto-optic tunable filters (AOTFs) and liquid crystal tunable filters (LCTFs). Preferably, liquid crystal imaging spectrometer technology is used for wavelength selection. A liquid crystal imaging spectrometer may be one or a hybrid of the following types: Lyot liquid crystal tunable filter (“LCTF”), Evans Split-Element LCTF, Solc LCTF, Ferroelectric LCTF, Fabry Perot LCTF. Additionally, fixed bandpass and bandreject filters comprised of dielectric, rugate, holographic, color absorption, acousto-optic or polarization types may also be used, either alone or in combination with one of the above liquid crystal spectrometers.
A number of imaging spectrometers, including acousto-optical tunable filters (AOTF) and liquid crystal tunable filters (LCTF) are polarization sensitive, passing one linear polarization and rejecting the orthogonal linear polarization. AOTFs are solid-state birefringent crystals that provide an electronically tunable spectral notch pass band in response to an applied acoustic field. LCTFs also provide a notch pass band that can be controlled by incorporating liquid crystal retarders within a birefringent interference filter such as a Lyot filter. Conventional systems are generally bulky and not portable. A handheld chemical imaging sensor capable of performing instant chemical analysis would represent progress in size, weight and cost reduction. Accordingly, there is a need for a handheld, portable and more efficient tunable filter.
Furthermore, there is a need to detect biothreat agents in the air, in water, and on surfaces in order to ward the first responder to don the appropriate personal protective equipment (“PPE”). However, currently there is no single, portable, instrument package that can detect biothreat agents in all three media and meet the desired ease of use and reliability requirements. Therefore, the detection of agents in samples of water and powders collected from the environment of a suspected biothreat incident scene is described herein.
Biothreat agents exist in four forms: agents such as anthrax are bacterial spores. Other biothreat agents exist as a vegetative (live) cell such as plague (Yersinia pestis). Another class of biothreat agents includes the virus responsible for diseases such as smallpox and Ebola. The final types of biothreat agent are toxins, chemicals produced by a specific organism that are toxic to humans, such as Ricin and botulism toxin. While these are technically chemical agents since they do not involve a living or dormant organism, they are typically considered as biothreat agents.
A practical biothreat detector must be able to identify as many different types of agents as possible. Ideally, it should cover agents in each of the four groups and should do so without the operator having any idea of which agent is present. This desired requirement effectively rules out the use of organism/toxin-specific reagents as used in DNA typing (e.g., PCR) and immunoassay techniques. Therefore, an approach to bioagent detection with no or minimal reagents or sample preparation is preferable in order to meet the needs of the first responder.
A practical handheld bioagent detector should preferably identify the presence of an agent in the presence of all of the other materials and chemicals present in the normal ambient environment. These materials and chemicals include dusts, pollen, combustion by-products, tobacco smoke, and other residues, as well as organisms normally present in water and soil. This detection specificity is desirable to avoid a false positive that can elevate a hoax into an apparent full-blown disaster, such as from a weapon of mass destruction.
Historically, reagent-intensive detectors have shown better specificity over reagentless techniques for bioagent detection. Part of this is due to the inherent selectivity in biological reagents. Every organism has many unique DNA segments that can be used for selective detection and identification. Immunological techniques rely on the extremely selective interaction between an antibody and its analyte organism or molecule. Coupling the DNA analysis or the immunology to a fluorescence detection scheme or an enzyme-linked color production provides excellent sensitivity in addition to this inherent selectivity.
In general, those reagentless techniques that have been successful for bioagent detection have used multiple measurements. For example, chromatographic techniques, which rely on time-resolved detection, have been used for bacterial identification based on the fatty acid distribution. Spatially resolved detection also has been shown to yield reliable detection of bioagents in the presence of clutter materials. However, specificity of detection is meaningless without enough sensitivity to detect a hazardous organism or toxin at or below a hazardous concentration. Unfortunately, these hazardous levels have not been well characterized for many biothreat agents, making the development of detection limits and effective detectors somewhat difficult.
Therefore it is desirable to develop adequate signal-to-noise for a handheld detector in order to detect a signal at a useful level. As in the case of selectivity, sensitivity is also helped by time-resolved and/or spatially-resolved measurements. For example, by taking measurements over several points on a sample (i.e., a spatially-resolved measurement) mathematical unmixing routines can be used to analyze the data and improve the effective signal-to-noise for detection.
Thus, there exists a need for rapid and reliable detection of biological agents by the first responder communities, which includes both military and civilian first responders as well as other public safety organizations. Current techniques for the detection of biological agents have the limitation of large size, high cost of consumables, limited ability to simultaneously detect more than one agent in a single test (i.e., limited multiplexing capability), long analysis times, limited sensitivity and susceptibility to false positive responses. All of these factors have prohibited current biothreat agent detectors from finding a role in the first responder, and similar, communities.
The first responder community needs a handheld biothreat detector that can be easily deployed by military and civilian first responders, has the ability to reliably detect multiple biothreat agents at sub-hazardous concentrations in actual environmental samples, and requires minimal logistical support. Additionally, it is desirable to have all of these features in an instrument package that is affordable to the first responder community. The present disclosure describes an apparatus and method that meets the needs of the first responder community.